Certain colored stones and crystals have been sought and prized for their beauty beginning with ancient civilizations and continuing into the modern age, even to the extent of ascribing to them magical powers. Through appropriate cutting and polishing, the value and natural beauty of a precious stone may be further enhanced. While a vivid color is not always a requirement for a jewel, i.e., cut stone, it is an important attribute of red ruby, blue sapphire or green emerald. Furthermore, the color or lack thereof may be an important attribute of relatively clear gems, such as diamonds.
Besides its visual beauty, a gemstone for ornamental purposes has to possess a certain amount of durability to be classified as precious, since it should be displayable by the owner without fear of deterioration or tarnish. Gemstones of the requisite hardness to qualify as durable include gem varieties derived from corundum (e.g., ruby, sapphire) and from carbon (e.g., diamond). Such gemstones typically not only outlive their wearers but also sparkle with undiminished luster long after their metal setting has been abraded or eroded.
Finally, naturally occurring gemstones generally are of higher inherent value than artificially grown gems, regardless of the fact that artificial stones often are of purer color and higher internal crystal quality. Although this result is probably attributable to the lack of rarity in the artificial stone, some minor flaws in naturally occurring stones are thought to add beauty and character to the final jewel.
Naturally occurring gemstones may exhibit undesirable color zones in which the color is distributed unevenly in the gem. The uneven color zones generally make it more difficult for the lapidary to select the direction in which the gem should be advantageously cut. On the other hand, colorless crystals often are less attractive than colored ones. Heat treatment of corundum to change its color or to remove some color zones has been practiced extensively. Other techniques, for example as disclosed in U.S. Pat. No. 4,039,726, consist of changing the color of corundum by diffusing chromophores such as iron/titanium, chromium, chromium/nickel, or chromium/iron/titanium into natural or artificial crystals at temperatures typically above 1700.degree. C.
There have been numerous attempts to combine colorless crystals with colored crystals, or to impart color by using dyed epoxy when setting or combining them. Although gemstones that are bonded with colored epoxy or other adhesives have reached a certain amount of popularity as fashion jewelry, they often are not as durable as desirable, and therefore cannot reach the quality of heirloom jewelry. Other techniques of combining crystals employ metal solders, brazes or mechanical means to hold crystals in place with respect to each other. A distinct disadvantage of this type of joining is the opaqueness of the bonding material that effectively separates the gems from each other.
Natural gemstones often exhibit such an intensive coloration that they appear black in larger sizes. To show their beautiful color to best advantage, they have to be faceted as smaller stones, which in turn reduces their rarity, value and effect. A prime example is Australian sapphire that has to be cut into small gems to show their blue color. In order to avoid cutting a large stone into small gems, intensely colored stones are sometimes cut into very shallow gems. Unfortunately the reduced gem thickness associated with this technique reduces the final jewel's brilliance due to the loss of light reflections.
A composite gemstone that combines the benefits of natural and artificially grown gems without suffering from the disadvantages associated with adhesive bonding is therefore desired.